Switching mechanism



Filed Dec. 31, 1942 4 Sheets-Sheet l \nnnnnnunn' lNl/ENTOR R. I: MALL/NA A rr'omvey Nov. 28, 1944. -R F. MALLINA SWITCHING MECHANISM Fil ed Dec.'31, 1942 4 Sheets-Sheet 2 FIG. 6

FIG. 5

lNl/ENTOR R. F MALL/NA A T TORNEV Nov. 28, 1944. R. F. MALLINA SWITCHING MECHANISM Filed Dec. 51, 1942 4 Sheets-Sheet 3 EEE:

Nov. 28, 1944. R. F. MALLINA 2,363,683

I SWITCHING MECHANISM Filed Dec. 31, 1942 4 Sheets-Sheet 4 FIG/2 wwmw A 7' TORNEV Patented Nov. 28, 1944 SWITCHING MEQHANiISM Rudolph F. Mallina, Hastings on Hudson, N. Y.

assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 31, 1-942, Serial No. 470,749

7 Claims.

This invention relates to switching mechanisms and particularly to such mechanism for use in automatic telephone systems.

I It is an object of the invention to simplify the construction of switching mechanisms of this kind to reduce the size and to permit the ,mechanism to be operated at a high speed.

. Heretofore switches have been used of the so- .called step-by-step type in which wipers are arranged .to contact with terminal banks by being advanced in steps in a vertical direction to select a horizontal row of terminals and then advance in steps in a rotary direction to engage a particular set of contacts in the selected row. .Switches of this kind may be provided with a carriage structure in which the wipers are mounted. This carriage is mounted on a ver- .tical shaft and provided with a toothed rack engaged by a stepping pawl operated by a magnet to raise the carriage and wipers to the desired row of terminals and provided with a ratchet wheel engaged by a stepping pawl operated by a magnet toadvance the carriage and the wipers in a rotary direction. To hold the carriage in advanced vertical position a holding pawl is provided for the rack. When the rack is rotated it is held by a fixed holding plate engaging a tooth in the rack and to hold the car- .ria e in .an advanced rotated position a holding .pawl is provided for engagement with the teeth in the ratchet wheel. The return of the carriage and wipers to normal may be accomplished by advancing them in the rotary direction to a last position where the rack will leave the holding plate and drop until the carriage and Wipers are fully returned vertically and then having the carriage engage the rotary holding pawl to release the ratchet wheel for the return of the carriage and wipers to normal position under tension of a spring.

The present invention relates to this latter type of switching mechanism and one feature relates particularly to arrangements for releasing the carriage and wipers to normal. This arrangement is such that as the carriage is advanced to the last position in a rotary direction for release, a pawl provided on the carriage engages a vertical guide bar so that when the carriage drops this pawl and guide bar serve as a holding means for holding the carriage inthis advanced rotary position until it has been completely returned vertically.

Another feature is an arrangement of a cam controlled by theratchet wheel when rotated to the last position to disengage the holding pawl from th ratchet wheel and thus permit the rotary release movement to begin immediately after the carriage has been fully returned in the vertical direction.

,An advantage of this arrangement of releasing is that the carriage is freed for release ro- .tar \y at the sam time that it is freed for release vertically and thus as soon as the vertical re.- lease has been completed the rotary release begins which .arrangement permits the return of the mechanism to normal with an increased speed.

Another feature is an arrangement of a switch .of this kind in which all the moving parts, such as the carriage, wipers and operating pawls and the magnets and armatures for actuating these pawls are mounted in a bracket which may be mounted on a frame containing the terminal banks in a position where the wipers will engage the terminals accurately when operated, and securely fastened in said positionmerely by a .single hand-operated screw. This feature is carried .out by having a projection below the lower side of the bracket engaging an aperture .in the. frame and having the upper end of the shaft extendin above the upper side of the bracket and enga ing a slot in the frame to secure the carriage in its proper position in front of the frame in ,a vertical position and having projections on the upper .member of the bracket engaging the frame on either side of the slot .to prevent the bracket from turning on the shaft and having .a single hand-operated screw mounted on the bracket on the upper member thereof and screwed into .a hole in the frame above the slot therein to tighten and hold the bracket and its mechanism securely and accurately in place.

The invention has been illustrated in the accompanying drawings in which:

Fig. 1 shows aside view of the switching mechanism mounted on a frame containin the terminals arranged in accordance with the apnlicantfs invention;

Fig. ,2 is a top cross section of this mechanism and frame taken on line 2-2 of Fig. 1;

Figs. 3 Lto ,6 are enlarged views showing vari- .ous positions taken by the ratchet wheel in the operation .of the mechanism Fig. '7 is a ,fragmentarycross section taken on line IF-l of Fig. ;1 ,with the carriage advanced .to the last rotary position;

Fig. .8 is a fragmentary perspective of the ipersand carriage .on the mounting shaft;

Figs. 9, .10 and .1 1 show various spring contacts operated during the operation of the mechanism, such as vertical off-normal contacts, rotary pulsing contacts and last step rotary contacts;

Fig. 12 is a fragmentary top view of the terminal frame and a stepping mechanism; and

Fig. 13 shows a circuit diagram for operating this stepping mechanism as a selector.

Referring now to the drawings, the wipers, carriage and operating magnets and pawls are all mounted on a bracket member I consisting of a vertical back or side portion 2, a horizontally located top member 3, a horizontal bottom member 4 and an intermediate right angle projection 5 extending from the back member 2. On this bracket or frame between the members 3 and 4 is mounted a shaft 6 the upper end of which is secured to the member 3 by means of a screw 1. This screw extends with its head above the member 3 as is shown in Fig. l. The lower end of the shaft is mounted in a sleeve or bushing 8 extending below the lower surface of member 4. On the shaft 6 is mounted a wiper carriage which consists of a bracket portion I!) terminating at the bottom in the horizontally located ratchet wheel II and at the top in the angular projection I2, through which two parts the shaft extends. Parallel with the shaft 6 is a rack I3 bent at the bottom into horizontal part I4 and at the top into a similar horizontal part I5, through which two parts the shaft 6 extends. The part I4 is provided with a right angle projection I6 and the part I5 is provided with a right angle projection I1 which projections are connected together by a bar I8.

On this bar I8 is mounted an upper set of wipers I9 and a lower set of wipers 2B. Wipers I9 are arranged for connection with sleeve terminals and wipers 20 with tip and ring terminals in the respective banks 2I and 22. Engaging a tooth on the rack I3 is a holding pawl which is mounted on frame member I while a stepping pawl 26 for the rack is mounted on an armature 21 which is pivoted at 28 to the yoke piece 29 for a magnet coil 30. mounted on a bracket 32 secured to the membar 2 and to hold the armature in its lowermost position normally a spring 33 is secured to the The yoke piece 29 is armature 21 and adjusted by means of a screw.

35 in a bracket 36 secured to the frame member 2. Pawl 26 is normally held in engagement with a stop member 31 by means of a helical spring 38 mounted on the pivotal pin 40 and when magnet 30 is energized its armature 21 will therefore advance the pawl 26 to engage a tooth in rack I3 to raise it one step. The rack will be held in this advanced position by the holding pawl 25. To regulate the stroke of pawl 26 a back stop M is provided and mounted on frame member 5.

Mounted on the lower member 4 of the frame is a magnet 42 by means of the yoke piece 43.

To this yoke piece is mounted on pivot 44, the

armature 45 at the end of which is mounted an operating pawl 46 on a pivot 41. This pawl is held against the stop 48 by means of a helical spring 49 mounted on the pivot 41. When the armature 45 is attracted by magnet 42 pawl 46 will engage the ratchet wheel II and rotate it one step. To regulate the stroke of the pawl 46 a backstop 50 is provided. To maintain the armature 45 in its normal position a spring 52 is attached at one end to the armature and at the other end is engaged by the screw 53 to regulate its tension. This screw is turnable in lugs 54 mounted on the lower frame member 4.

Surrounding the shaft 6 at its upper end is a helical spring 56 one end of which is secured to the frame member 3 at the top and at the lower end secured to the projection I5 of rack I3 so that when the rack has been lifted the spring will to some extent help in returning it to normal in the vertical direction and also when the ratchet wheel is free for rotation back to normal this spring will furnish the moving power for this purpose. The rack I3 engages a. slot in the upper angular projection I2 of the bracket member II). This slot is marked 58 in Fig. 8, the only figure in which it is clearly shown. Therefore, when the ratchet wheel II rotates the rack I3 will rotate with it, while being free to move in a vertical direction in the slot 58. Between the ratchet wheel II and the sleeve 8 is mounted a cam member 60 which normally stands in the position shown in Fig. 3, as it is held in this position by pin 62 projected downwardly from the ratchet wheel II. Associated with the ratchet wheel II and mounted on the lower member 4 is a spring-tensioned holding pawl 63 normally engaging a tooth in the ratchet wheel I I.

Referring now to Figs. 1 to 8 in particular, a description will be made of the operation of the mechanism so far described. When the magnet 36 is energized the armature 21 causes pawl 26 to engage the rack I3 and raise this rack and wipers I9 and 20 one step, while the holding pawl 25 maintains the rack in this advanced position. This operation may be repeated until the desired level of terminals is reached. Then the magnet 42 is operated to cause its armature 45 and pawl 46 to engage a tooth in the ratchet wheel I I which is then advanced one step from the normal position determined by a stop pin 64 (Fig. 3) engaging the ratchet wheel II in this normal position. This operation may then be repeated until the wipers have been advanced to a particular set of terminals in the selected level. The ratchet wheel II is held in the operated positions from tooth to tooth by means of the holding pawl 63. As stated the rack I3 rotates with the ratchet wheel II. Thus on the first rotary step the rack I3 will leave the holding pawl 25 but a tooth in this rack will now be engaged by the holding plate 66 so as to maintain the rack and wipers in the elevated position.

The switch remains now in this position until it is desired to releas it to normal position and a description of th operations to release the switch will now be made. When it is desired to release this connection the magnet 42 is again energized to cause the armature 45 and pawl 46 to advance the ratchet wheel I I to a position where the wipers are placed beyond the last set of terminals in the selected row. In this case it would be at the eleventh step of the magnet and ratchet wheel. At this time the tooth in rack I3 that engages the holding plate 66 has been shifted beyond this plate as shown in Figs. '1 and 8 and is. thus free to restore to its normal position in the vertical direction. However, to hold the rack and wipers in this advanced rotary position while they descend vertically two operations take place. One is that a pawl 69 on the projection I5 of the rack I3 has now passed a vertical holding plate 10, secured to the member 5 of the frame, so that the hook-shaped end of this pawl will now under tension of spring 1I engage the plate on the front side looking at Fig. 1 and hold the rack and wipers in this poaaesgeas sition, -Thespring11 is attached atone end to an extension on pawl-69 and at the other end to the projection I 5. The second operation that takes place is that the pin 82 on the ratchet wheel I I will engage one edge of the cam 68 and rotate thiscam in a clockwise direction. until it takes the position as shown in Fig. where it is'stopped by pin 64. When this takes place the cam portion I3 at the opposite side of the cam will engage the holding pawl '63- and cause it torelease the ratchet wheel II. Under these circumstances therefore th ratchet wheel is now ready to return to its normal position from the rotary movement but is prevented from doing this by the pawl 89 engaging the plate I8 until the rack It has: returned fully in its vertical directi'on. When this position is reached the pawl 89- will slip off the lower end of the: plate I8 and thus permit the ratchet wheel II with rack I3" and the wipers to return to normal position; under the tension of spring 6. This position is shown in Fig. 3. It will be noted as shown in Fig. 6 that just prior to the return of wheel II completely to the normal position the pin 62 will again engage the cam 88 at the point 15 and thus rotate the cam in the counter-clockwise direction to remove the projection I3 from the pawl 68and thus permit this pawl to be restored at the same time as the ratchet wheel II is restored to normal as shown in Fig 3. Fig. 4 shows the position of the ratchet wheel in an intermediate advanced position before it has been rotated fully to the eleventh position. Thus it will :be seen that the restoring of the mechanism may take place with the least possible delay at the moment the ratchet wheel has been rotated to the eleventh position as both the rack I3 and the ratchet wheel H are freed from their holding means, rack I3 from. the plate 66 and the ratchet wheel II from the holding pawl 63 so that on the return vertically of the rack the rotary return may immediately begin without having to wait fo-rthe release of the ratchet wheel II from its holding pawl.

The rotary magnet 42 may be operated by circuits closed through self-interrupting contacts by an arrangement of such contacts as shown in Fig. particularly. That is, each time the armature 45 is operated it will engage a projection II-extending from spring I8 to have the spring open its connection with a spring I9. Other spring contacts may also be provided, for exammember I8 of the carriage. When therefore the rack I3 is lifted this pin 85 releases the projection 84 permitting the lever 8| to rotate looking at Fig. 9 in a clockwise direction to permit the springs 88 to close, the upper one of these springs being under tension for this purpose. Then when the rack is returned to normal in the vertical direction and the ratchet Wheel II returns it in a rotary-direction, the pin 85 will engage projection 84 from the left-hand side thereof and return it to normal to open the springs 88. A somewhat similar arrangement is provided for other springs as shown in Fig. 11 which are operated on the last rotary step of the ratchet wheel I I. These springs are shown in Fig. 11 at 98 and may be operated by a lever in pivoted at 92 in the bracket 82'. The opposite. end: of this lever 9I is bent upward and then towards the left into an end piece 93 looking at Fig. i1 and extends through an opening in. the member 4 of the frame. I This end piece 93 is. engaged by pin 84 on the ratchet wheel II when the ratchet wheel takes the eleventh step to rotate the lever SI to operate contacts 98.

This mechanism as hereinbefore described for operating the wipers to select a particular set of terminals and be returned to a normal position is arranged in a very compact manner inside the members 2 to 5 of frame I. This unit may therefore be easily and speedily associated with the terminal banks 2I and 22 to accurately place the wipers in position for engagement with the ter-- minals in these banks by a simple arrangement which will now be described. It should be noted that the sleeve 8 extends slightly below the plate 4 and may be engaged in an opening I88 in a projection I8I from the lower plate I82 of the terminal bank assembly and that the screw 1 engages the slot I84 in projection I85 on the upper plate I86 of the terminal bank assembly. This projection I85 has the angular cut-out projection or member I8!- in which the screw I88 may be secured. This screw is mounted in openings in the brackets I89 and H8 and has a knob III at its right-hand side looking at Fig. 1 which when the screw is fully inserted in the projection I 81 has its shank or hub II2 engaging the outer surface of the bracket I I 8. A holding ring or enlargement H5 is provided on the screw I88 to prevent it from falling out from its bearing brackets I89 and H8 when not inserted in the projection I81. It should be observed that in order to mount this mechanism on the terminal assembly between the members I8I and I85 the mechanism is, first arranged so that the sleeve 8 engages in the hole I08'and then the mechanism is tilted or advanced so that the screw I enters the slots I84. When this is done the screw I88 is inserted in projection I81 and screwed in by turning by hand the knob III and tighten it to securely press the mechanism in place. This positions the shaft 6 in proper relation to the terminal banks so that one vertical step of the wipers will place them opposite the first level of terminals. To position the wipers accurately so that one step in a rotary direction will place them on a first set of terminals, members H8 and I I9 are provided. These members extend in opposite directions from the bracket I89 and engage the outer edge I28 of the projection I85. By accurately positioning these members I I8 and the edge I28 and accurately gauging the size of the sleeve 8 in the hole I88 as Well as the width of the slot I84 and the size of the screw 1 the mechanism may therefore be accurately placed in position where the wipers will engage the terminals properly when raised and rotated.

As shown in Fig. 12 in particular, the arrangement of these operating mechanisms in relation to the terminal banks may be such that a pin-- rality of mechanisms may be mounted in rows on opposite sides of the bank assembly, that is, the terminals may be duplicated in rows on opposite sides in the frame members I86 and I82 which may extend to accommodate a considerable number of switching mechanisms.-

In Fig. 13- a circuit arrangement has been shown for telephone systems in which applicant's switch may be incorporated and the part of the circuit in which the mechanism serves as a selector has been shown in detail. A description of this circuit will now be made.

A calling subscribers station indicated at I36 terminates in a line finder I3I which may be operated in any well-known manner to establish a connection to the selector circuit I32. When this connection is established, a circuit is completed for the operation of relay I33 from battery through the upper Winding of this relay, contacts of relay I34, over the tip conductor, line finder 'I3I and the subscribers loop back over the ring conductor, line finder, contacts of relay I34 and the lower Winding of relay I33 to ground at the eleventh step contacts 96. Relay I33 closes an obvious energizing circuit for relay I35 and the subscriber may now dial the first digit of the desired number and thereby cause the repeated operation and release of relay I33. Relay I35 remains operated during this pulsing. On the first release of relay I33, a circuit is completed for the vertical magnet 36 from battery through the winding of this magnet, contacts of relays I35, I33 and I34 to ground. Relay I36 is also operated from battery through th winding of this relay, contacts of relays I35, I33 and I34 to ground. Relay I36 remains operated during the pulsing. After the first step of the vertical magnet, the vertical off-normal contacts 86 are closed and a circuit is completed for the operatic-n of relay I31 from battery, winding of this relay, vertical cit-normal contacts 86, contacts of relays I36 and I35 to ground. Relay I31 is looked over a circuit from battery through the winding of this relay, vertical off-normal contacts 86, contacts of the rotary magnet 42, contacts of relays I31 and I34 to ground. When this digit has been dialed and relay I36 releases as well as the vertical magnet 36, a circuit is completed for the rotary magnet 42 from battery, winding of this magnet, contact of relays I31, I36, I35 to ground. The rotary magnet opens the locking circuit for relay I31 which new releases causing the release of the rotary magnet 42. If the brushes I46 of the selector land on terminals of a busy connectorcircuit which has been indicated diagrammatically at I42, a ground will be present on the sleeve terminal of the connector. Thus a circuit will be completed for the reoperatio-n of the relay I31 from battery through the winding of this relay, vertical off-normal contacts 86, contacts of rotary magnet 42, contacts of relay I34 to this ground on the sleeve terminal. Relay I31 closes a circuit for the rotary magnet which now operates and causes the release of relay I31 which releases the rotary magnet 42 and the brushes I46 are then stepped to the terminals of the next connector. These operations are repeated until an idle connector circuit is found when relay I34 will operate from battery, winding of relay I31, vertical off-normal contacts 86, contacts of magnet 42, winding of relay I34, contacts of the eleventh step rotary contact 96 to ground at contacts of relay I35 or on the sleeve to the line finder I3I.

Relay I31 does not operate in this, circuit. Relay $34 in operating, opens the cir- .a

On the release of this relay the release of the selector will be initiated by a circuit for the rotary magnet 42 from battery, the winding of this magnet and the self-interrupting contacts 18 and 19, vertical off-normal contacts 86, contacts of relay I44, eleventh step rotary contacts 96, contacts of relays I35 and I34 to ground. The rotar magnet 42 will not alternately operate and release due to the self-interrupting contacts 18 and 19 opening and closing its circuit. When the rotary magnet has advanced the wipers and the rack I3 to the eleventh position, the contacts 96 will be actuated. These contacts then will close a circuit for the relay I44 from battery through the winding of this relay, contacts 96,

contacts of relays I35 and I34 to ground. This relay I44 will then lock over an obvious circuit through the vertical off-normal contacts 86. The contacts 96 as well as the contacts of relay I44 are now opened to open the circuit for the rotary magnet 42 so as to discontinue the operation of this magnet and in accordance with the description heretofore made, the rack and wipers will return to the normal position vertically and when in this position the vertical off-normal contacts 86 will be restored opening the locking circuit for relay I44 which is released. The contacts 96 will, of course, be restored to normal position when the rotary return of the ratchet wheel II begins.

What is claimed is:

1. In a switching mechanism, a brush carriage mechanism, means for operating said carriage to lift it and then rotate it to a desired position including a horizontal stationary member engaged by said carriage to retain it in its lifted position during its subsequent rotary movement and a pawl engaging said carriage to retain it in its rotated position, means operative in response to the rotation of said carriage to a certain advanced position for releasin said carriage from the stationary member and the rotary retaining pawl simultaneously to return it from the lifted position and then immediately to return it from the rotated position, said means including a vertical stationary member and a pawl engaging it to guide the carriage during the vertical return movement and a cam operative to free the carriage from the rotary retaining pawl.

2. In a switching mechanism, a vertical shaft, a ratchet wheel mounted on said shaft, a brush carriage mounted on said shaft and arranged to rotate with said ratchet wheel but being free to move longitudinally upon said shaft and having a vertically located toothed bar, means for moving said carriage vertically in steps through the medium of said toothed bar, means for moving said carriage in a rotary movement in steps through the medium of said ratchet wheel, means for holding said carriage in the position to which it has been moved vertically during the subsequent rotary movement and through the medium of said toothed bar, means for holding said carriage in the position to which it has been moved in a rotary direction through the medium of said ratchet wheel, means operative by said ratchet wheel when advanced to a certain position for releasing said ratchet wheel from said holding means, means operated by said carriage when rotated to said certain position for preventing it from rotating back to normal, said carriage being arranged when advanced to said certain position for freeing the toothed bar from the means that held it in its vertical advanced position and thus return it to its vertical normal position and on its return to said position freeing itself from the means that held it in said certain position in the rotary direction and thus return it to its rotary normal position.

3. In a switching device, a brush carriage including a vertical toothed bar and a horizontal ratchet wheel, means for operating said carriage to lift it through the toothed bar and rotate it through the ratchet wheel, a horizontal plate engaging said toothed bar when the carriage is being rotated to retain the carriage in its lifted position, a retaining pawl engaging said ratchet wheel to retain the carriage in its rotated position, a pawl on said carriage and a stationary vertical rib cooperating when the carriage has been rotated to a certain advanced position where the toothed bar is freed from the horizontal plate for guiding said carriage on its return to normal in a vertical direction, a cam controlled when the carriage has been rotated to said certain advanced position for freeing the ratchet wheel from said retaining pawl, to permit the carriage to return to normal position in the rotary direction after it has returned in its vertical direction.

4. In a switching mechanism, a bank of terminals, an upper and alower mounting plate for said bank, a frame, a brush carriage in said frame, means in said frame for advancing said brush carriage to cause its brushes to engage terminals in said bank, a projection on said frame engaging an aperture in said lower mounting plate, a projection on said frame engaging a slot in said upper mounting plate, a screw having a knob and mounted in said frame so that said screw when rotated by said knob may be secured into a threaded hole in the upper mounting plate to hold the frame securely to the mounting plate, and a guidemember on said frame to accurately place the frame in position on the mounting plates so that the brushes of said carriage are placed in position to accurately engage the terminals in said bank when said carriage is moved.

5. In a switching mechanism, a bank of terminals, an upper and a lower mounting plate for said bank, a frame, a brush carriage in said framexmeans in said frame for actuating said brush carriage to cause its brushes to engage terminals in said bank, means for mounting said frame in position between said plates to accurately place the brushes of said carriage to correctly engage the terminals of said bank when the carriage is moved, said means including a projection on the frame engaging an opening in one of said plates and another projection on said frame engaging in a slot in the other plate and a single hand-operated screw to secure the frame to the plates.

6. In a switching device, a brush carriage ineluding a vertical toothed bar and a horizontal ratchet wheel, a spring for holding said carriage in a normal position, means for operating said carriage to lift it through the toothed bar and rotate it through the ratchet Wheel against the tension of said spring, a horizontal plate engaging said toothed bar when the carriage is being rotated to ,retain the carriage in its lifted position, a retaining pawl engaging said ratchet wheel to retain the carriage in its rotated position, a pawl on said carriage and a' stationary vertical rib cooperating when the carriage has been rotated to a certain advanced position where the toothed bar is freed from the horizontal plate for guiding said carriage on its return to a normal position in a vertical direction under tension of said spring, a cam operated by the ratchet wheel when advanced to said certain position to disengage said retaining pawl for freeing said ratchet wheel so that when the carriage has been returned to its normal position in the vertical direction, the carriage will be free to return to its normal position in the rotary direction under tension of said spring.

7. In a switching mechanism, a frame comprising an upper and a lower mounting plate, said plates being located in parallel relation to each other, terminals mounted between said plates and arranged in groups so as to protrude for contacting purposes on opposite sides of said plates, a series of switch frames, each being located between said mounting plates and of the same width as the distance between these plates, each switch frame being located opposite a particular group of terminals, a carriage with wipers mounted on each switch frame and means in each switch frame for actuating said carriage to cause the associated wipers to engage the associated group of terminals, means for mounting each switch frame in position on said plate so as to accurately place the Wipers when moved in engagement with the associated terminals, said mounting means comprising a lower projection on said switch frame fitting tightly in an opening in the lower plate and a similar upper projection on said switch frame fitting tightly in a slot in said upper plate, a screw mounted on the upper side of the switch frame arranged to be screwed into said upper plate to securely fasten the switch frame to said plates and guide members on the sides of said switch frame engaging the upper plate, said projections, opening, slot and guide mem bers being so fitted and cooperating that the wipers when moved will accurately engage the associated terminals.

RUDOLPH F. MALLINA. 

